The present invention relates to a technique of manufacturing a wound coil for use in, for example, an electromagnetic clutch which enables or disables transmission of the power to a compressor in an automobile air conditioner. More particularly, this invention relates to a coil bobbin and a winding jig for use in forming the wound coil and a method of winding a wire on the coil bobbin.
Upon forming a coil by winding a wire, a coil bobbin may be used or may not be used.
When the coil bobbin is not used for forming the coil, the wire is directly wound around a jig to obtain the wound wire which is then detached from the jig in this state. Thereafter, for keeping the wound wire in shape, an insulating tape is twined around the wound wire at some portions thereof or along the whole circumference thereof, and then a cotton tape is further wound thereon.
On the other hand, when the coil bobbin is used for forming the coil, the wire is wound around the coil bobbin to obtain the wound wire which is then temporarily retained using a tape or the like.
In the former case, since the operation of twining the insulating tape around the wound wire is troublesome, the production thereof is not easy. Further, since the wound wire easily gets out of shape and the insulation property is poor, the low reliability is resulted. On the other hand, in the latter case, since the operation of twining the insulating tape is not required and further the wound wire does not get out of shape so that it is excellent in insulation property, the high reliability is resulted. In view of this, the coils using the coil bobbins have been dominant recently.
The conventional coil bobbins are generally made of nylon resin. The coil bobbin comprises a tubular portion, a first flange portion outwardly extended from one axial end of the tubular portion and a second flange portion outwardly extended from the other axial end of the tubular portion. The outer periphery of the tubular portion and the inner surfaces of the first and second flange portions define a wire winding region or a coil-placing region where the wire is wound.
The conventional coil bobbins are classified into a first and a second type. In the first type, the outer periphery of the tubular portion is formed with grooves for facilitating the wire winding as disclosed, for example, in JP-A-5-258940. In the second type, the outer periphery of the tubular portion is not formed with a means for facilitating the wire winding.
When the coil bobbin of the second type is used, it is difficult to wind the wire in an orderly manner so that the disorder in winding is resulted. For preventing an occurrence of the winding disorder, the dimensions of the wire winding region, particularly a width (an interval between the inner surface of the first flange portion and the inner surface of the second flange portion) thereof, are important. Since an adjustment of the width is not possible in the coil bobbin, the width of the coil bobbin should be achieved in advance with high accuracy. However, since the coil bobbins are generally made of nylon resin, the dimensional accuracy is not so high. For enhancing the dimensional accuracy, the production cost is increased.
On the other hand, the coil bobbin of the first type has the following problem. Specifically, on metal molds for forming the coil bobbins of this type, concave-convex portions are provided for forming the grooves. When the resin is poured into the metal molds, the concave-convex portions are abraded due to friction between the concave-convex portions and the resin. The abrasion of the concave-convex portions is particularly severe on joining surfaces of the metal molds so that the metal molds become unusable immediately. Accordingly, the life duration of the metal molds is short and thus the high production cost of the coil bobbin is resulted.